【判断题】Chemical milling is controlled etching process using strong alkaline or acid etchants. Aluminum, titanium, magnesium, and steel are the principal metals processed by this method. 化学蚀刻,通过使用强碱或强酸蚀刻剂来控制蚀...
【单选题】听力原文:Watching his mother drown and then clinging to an inner tube for two days were painful enough. And psychologists say Cuban boy Elian Gonzalez's anxiety is probably being worsened by the persisten...